The present invention concerns a plastic screw closure for bottles, comprising a substantially cylindrical peripheral portion with an internal screwthread for screwing onto the external screwthread of a bottle neck, and a top plate portion which is substantially in the form of a circular disc and a substantially cylindrical sealing strip which extends axially inwardly from the inside of the top plate portion and whose outside diameter approximately corresponds to the outside diameter of the bottle neck or is slightly larger and whose inside diameter is clearly smaller than the outside edge of the bottle neck.
A plastic screw closure of that kind for bottles is already known from DE 41 28 474.
The known plastic screw closure is intended for screwing onto the screwthreaded neck of bottles and is of such a design configuration that the substantially cylindrical strip bears from above and the outside onto the edge of the bottle neck and in so doing bears sealingly substantially along the upper outer rounded-off edge of the bottle neck or the mouth of the bottle. In that arrangement, the sealing strip is additionally also clamped between an outer substantially cylindrical bead or ridge and the bottle neck and is pulled and pressed into firm sealing engagement with the edge of the bottle neck. In principle such a closure could also be used for plastic bottles, for example PET-bottles.
In the case of multi-use bottles made of glass, the bottles generally and in particular also the bottle necks and mouth openings are visually checked before they are reused. In that respect however the possibility cannot be excluded, that damage to the edge of the bottle neck in the region where it comes into sealing engagement with the closure cap or sealing elements of the closure cap is overlooked, particularly if such damage is relatively small and inconspicuous. In principle that also applies for plastic bottles, in particular for the PET-bottles which are increasingly used. When dealing with plastic bottles, under some circumstances, due to the production procedure involved it is also necessary to reckon on rather larger manufacturing tolerances or damage occurring in the course of manufacture or handling. Minor damage, in particular in the form of small dents or grooves, can only be visually detected with difficulty. It can therefore certainly happen that bottles are filled and closed, when the edge of the bottle neck thereof has suffered minor damage, deformation or unevenness and irregularities caused by the manufacturing procedure and which are easily overlooked in a checking operation but which are sufficient to have an adverse effect on the sealing engagement between the edge of the bottle neck and sealing elements of the closure cap. That applies in particular if the interior of the bottle is under pressure, for example when using the bottles for carbonated drinks. A poor seal in the case of such bottles can have the result that gas escapes from the bottle and as a result causes a drop in pressure, which in turn results in outgassing of the carbon dioxide contained in the drink, which then after a storage time of some days or weeks, has substantially lost its carbon dioxide and correspondingly tastes stale.
WO 96/02430 already discloses a closure cap which is intended to ensure particularly good sealing engagement. Instead of a substantially cylindrical sealing strip, this known closure cap however has a substantially horizontally extending sealing strip which bears against the upper edge of the bottle neck, while in addition annular projections are provided at the bottom or the top plate portion of the closure cap and are intended to come into engagement with the sealing strip on the side thereof in opposite relationship to the edge of the bottle neck, and apply a linear sealing pressure to the sealing strip. The arrangement additionally also has an inner substantially cylindrical sealing olive, in which respect the term "olive" clearly defines the lower cross-section of that part which has an outwardly projecting region which is also intended to come into substantially linear engagement with the cylindrical inside surface of the bottle neck. Admittedly, the inside surface of a bottle neck is generally fairly precisely defined, at least in the case of PET-bottles, but it may certainly involve damage, so that the projection of the sealing olive cannot guarantee reliable sealing integrity, in spite of the substantially linear engagement of the sealing olive with the interior of the bottle neck. In addition, the sealing projection of the known closure is disposed at a considerable spacing relative to the point of attachment of the sealing plate portion to the top plate portion so that the arrangement does not afford very high elastic return or contact pressure forces in the region of the projection.
A substantially radially extending sealing plate admittedly partially covers over the outer, generally well-defined, rounded-off edge of the bottle neck which however can also be damaged, but just like the sealing olive it does not involve the inner, slightly rounded-off edge configuration of the edge portion of the bottle neck. These parts which are positioned in different ways relative to the axis of the closure define a blind hole-like depression with a considerable undercut configuration which gives rise to major problems in manufacture and in the operation of pressing out air, which is required in that context.
WO 96/26121 discloses a corresponding screw closure which, besides a substantially conically outwardly directed, peripherally extending sealing plate which is intended to come into engagement with the outer edge of the bottle neck, additionally also has an inner centering projection whose outside diameter however is somewhat smaller than the inside diameter of the bottle neck. That projection therefore does not come into sealing engagement with the interior of the bottle neck and in particular not with the upper inner edge of the bottle neck.
Because of the conical shape of the sealing plate, removal of such a closure from an injection moulding tool is a relatively difficult and complicated procedure. That applies even more in regard to the above-mentioned closure disclosed in WO 96/02430 in which the sealing plate extends parallel to the top plate portion radially inwardly virtually in one plane and, together with a further inwardly disposed sealing olive, defines a virtually closed hollow space or cavity.
The known closures therefore have at least in part problems in terms of manufacture and in particular removal from a mould and on the other hand they still do not guarantee absolutely sound sealing integrity in the event of minor damage or deformation of the edge of the bottle neck.